How to make blurred smoke enough visible with an orange background
The two things that are most likely to help are density and colour. 

In your smoke shader, run the density factor through a math node. Use either multiply or power with a value that suits your taste. 

Also, use a colour with better contrast against orange. Blue would be my choice since it's opposite to orange. 

Okay, here's the changed portion of the node tree:


Notice the frames labelled "Smoke colour" and "'Density' multiplier". It is that transparency shader which lends the contrasting colour to the smoke against the background, effectively filtering the colour.

The density multiplier allows fine control of the smoke texture's rendering. By first multiplying the value various pixels can be moved above or below a value of 1.0. Passing this through a power (read: exponential) node then amplifies the gradient.

Updated .blend